Methods and apparatus for flexible spectrum allocation in communication systems

ABSTRACT

The disclosed embodiments provide for methods and systems for flexibly allocating a shared frequency spectrum to a plurality of users, the spectrum may have a first number of segments, each segment having a second number of clusters associated with a certain sector/cell. In one aspect, a method for flexibly allocating a shared frequency spectrum to a plurality of users comprises the acts of fixedly assigning a first group of clusters to a first group of users, such that the first group of users stay fixed to the assigned clusters, and assigning a second group of clusters to a second group of users, such that the second group of users hop within the assigned clusters.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present Application for Patent claims priority to ProvisionalApplication No. 60/554,899 entitled “Flexible Spectrum Allocation inOFDMA” filed Mar. 19, 2004, and assigned to the assignee hereof andhereby expressly incorporated by reference herein.

BACKGROUND

I. Field

The present invention relates generally to communications and morespecifically to techniques for flexible spectrum allocation to aplurality of users in a communication system.

II. Background

Communication systems are widely deployed to provide variouscommunication services such as voice, packet data, and so on. Thesesystems may be time, frequency, and/or code division multiple-accesssystems capable of supporting communication with multiple userssimultaneously by sharing the available system resources. Examples ofsuch multiple-access systems include Code Division Multiple Access(CDMA) systems, Multiple-Carrier CDMA (MC-CDMA), Wideband CDMA (W-CDMA),High-Speed Downlink Packet Access (HSDPA), Time Division Multiple Access(TDMA) systems, Frequency Division Multiple Access (FDMA) systems, andOrthogonal Frequency Division Multiple Access (OFDMA) systems.

A communication system may employ bandwidth allocation to avoidinterference and improve link reliability. There is therefore a need inthe art for techniques for flexible bandwidth allocation that improvesinterference.

SUMMARY

The disclosed embodiments provide for methods and systems for flexiblyallocating a shared frequency spectrum to a plurality of users. Thespectrum may have a first number of segments, each segment having asecond number of clusters associated with a certain sector/cell. In oneaspect, a method for flexibly allocating a shared frequency spectrum toa plurality of users comprises the acts of fixedly assigning a firstgroup of clusters to a first group of users, such that the first groupof users stay fixed to the assigned clusters, and assigning a secondgroup of clusters to a second group of users, such that the second groupof users hop within the assigned clusters, is described.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and nature of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings in which like reference charactersidentify correspondingly throughout and wherein:

FIG. 1 shows one embodiment for frequency spectrum partitioning;

FIG. 2 shows one embodiment for flexible frequency spectrum allocation;and

FIG. 3 shows a block diagram of an access point and an access terminal.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment or design described herein is“exemplary” and is not necessarily to be construed as preferred oradvantageous over other embodiments or designs.

An “access terminal” refers to a device providing voice and/or dataconnectivity to a user. An access terminal may be connected to acomputing device such as a laptop computer or desktop computer, or itmay be a self contained device such as a personal digital assistant. Anaccess terminal can also be called a subscriber unit, mobile station,mobile, remote station, remote terminal, user terminal, user agent, oruser equipment. An access terminal may be a subscriber station, wirelessdevice, cellular telephone, PCS telephone, a cordless telephone, aSession Initiation Protocol (SIP) phone, a wireless local loop (WLL)station, a personal digital assistant (PDA), a handheld device havingwireless connection capability, or other processing device connected toa wireless modem.

An “access point” refers to a device in an access network thatcommunicates over the air-interface, through one or more sectors, withthe access terminals. The access point acts as a router between theaccess terminal and the rest of the access network, which may comprisean IP network, by converting received air-interface frames to IPpackets. Access point also coordinates the management of attributes forthe air interface.

FIG. 1 shows one embodiment for frequency spectrum partitioning. Theforward link (FL) and/or the reverse link (RL) channel frequencyspectrum, e.g., in an OFDMA system, may comprise of N orthogonalsub-carriers or tones. In one embodiment as shown in FIG. 1, one maypartition the set of N tones into N_(s) segments 102, each segmenthaving a size of M_(s) frequency tones. In one embodiment, the segmentsare contiguous in frequency spectrum, while other arrangements are alsopossible.

In one embodiment, each segment is subdivided into a set of N_(c)clusters 104, each of size M_(c) tones, associated with each sector/cell108, 110. In one embodiment, the clusters associated with a sector/cellhave non-overlapping sub-carrier assignments. In the example given inFIG. 1, the segment size is M_(s)=32 tones and at least one segment,e.g., the first segment 106, is partitioned to N_(c)=4 clusters of sizeM_(c)=8 tones for each sector/cell 108, 110, although it is contemplatedthat any number of tones and/or clusters may be used. The clusters 104shown in FIG. 1 have non-contiguous, non-overlapping sub-carrierassignment patterns for each sector/cell 108, 110, and the adjacentsectors/cells in the network have different cluster patterns. Accordingto one embodiment, each of the clusters associated with a sector/cell,e.g., sector 108, is different with respect to each of the clustersassociated with another sector/cell, e.g., sector 110.

In one embodiment, the same cluster pattern set is used for some or allsegments in a given sector/cell, and such cluster pattern may be used asa characteristic of the sector/cell. The cluster pattern set may bedefined by an ID, including segment ID and/or cluster ID, which may becommunicated to the access terminal (AT) in the acquisition phase, oralternatively linked to the acquisition signature of the sector/cell. Anappropriate design of cluster pattern set improves user interferencediversity, as discussed below.

In one embodiment, a given cluster (sub-channel) in a given segment maybe allocated to a user, as shown in FIG. 1. Alternatively, more than onecluster in a given segment or more than one cluster in more than onesegment may be allocated to a user. In the example of FIG. 1, theallocation granularity is M_(c)=8 tones, although it is contemplatedthat the allocation granularity may be any number of tones. A user maybe assigned multiple clusters in a single or multiple assignments. Moredetails on the assignment strategy are given below.

In one embodiment, every user may be provided with a control channel oran item sent in the control channel, e.g., channel quality indicator(CQI), for every segment. The CQIs may be computed from the channelcharacteristics acquired for some or all tones. The resulting CQI persegment may be obtained, for example, by averaging the quality measures,such as SNR, Shannon capacity, etc., of some or all the tones from thatsegment.

In one embodiment, following a certain channel sensitive scheduling(CSS) criterion, the “best” match between a given segment and a user isidentified. In one embodiment, channel information on the RL and/or FLmay be used to schedule users to one or more segments of a sharedfrequency spectrum. A scheduler may assign the user one or moreclusters, provided that at least one cluster is vacant. Such anassignment may be based on, and may be expected to secure, a goodchannel quality, e.g., measured in terms of channel gain. Upon theassignment, the user may be exposed to various interfering usersoperating in the adjacent sectors/cells. The disparity of clusterpattern sets corresponding to different sectors/cells, as discussedabove in connection with FIG. 1, ensures that no user or a small numberof users is exposed to a single interfering source, thereby ensuringinterference diversity.

In the example shown in FIG. 1, any cluster associated with a givensector/cell 108 overlaps with each one of clusters associated with anadjacent sector/cell 110 in an equal amount of bandwidth or number oftones. For the current example, such clusters overlap in two tones, butdiffer in six. Thus, the disclosed partitioning, e.g., N_(c)=4 clustersand one user per cluster, as shown in FIG. 1, improves interferencediversity. In a similar way, cluster pattern sets for the other adjacentsectors/cells may be designed to ensure full interference diversity.Full interference diversity condition described above assumes that nouser is assigned two or more clusters within the same segment. Ingeneral, a user may be assigned two or more clusters within the samesegment, e.g., when a single user is assigned a substantial fraction ofthe entire shared bandwidth, as discussed later.

The aforementioned example provides an example as how to ensurechannel-sensitive scheduling (CSS) with interference diversity.Following this principle, one can achieve a desired tradeoff between thechannel assignment granularity, interference diversity, and CSSefficiency by choosing the appropriate values for N_(s), M_(c), andN_(c). The disclosed bandwidth allocation strategy may not introduce anyoverhead in assignment bandwidth, as compared to other bandwidthallocation techniques.

In one embodiment, the total number of bits that may be used for abandwidth allocation is ┌log₂(N_(s))┐+┌log₂(N_(c))┐. In one embodiment,bandwidth partitioning is “compact” in the sense that no tones arewasted, so thatN _(s) ·N _(c) ·M _(c) =N.

In this case, one obtains ┌log ₂(N_(s))┐+┌log₂(N_(c))┐≦┌log₂(N/M_(c))┐+1, while ┌log₂(N/M_(c)) is the minimum numberof bits required to allocate a cluster comprising M_(c) tones in asystem with N tones, assuming non-overlapping tones.

In one embodiment, channel quality information on the RL and/or FL maybe used to schedule users on a shared frequency spectrum, e.g.,according to CSS scheduling approach discussed above. In the case ofnomnoving or slow-moving user terminals, when the channel quality wouldnot change, or changes very slowly, e.g., a pedestrian user, CSSapproach may be used. In one embodiment, at least one of a first groupof clusters of frequency sub-carriers is fixedly assigned to each of afirst group of such users. In such a static or fixed assignment, whereeach of the first group of users is non-moving or slow moving, each ofthe first group of users is fixedly assigned to at least one of thefirst group of clusters until the user is reassigned, e.g., due to achange in the channel quality, speed, Doppler, or an indication, e.g.,NACKs, that some packets are not being received.

In one embodiment, the shared frequency spectrum may be allocated to asecond group of users that may have varying degree of mobility and/orchannel quality, or when frequent NACKs are being received. In oneembodiment, e.g., in the case of fast moving user terminals and/or usersexperiencing Doppler effect, e.g. a vehicular user, frequency Hopping(FH) approach may be used to compensate for fast variations in thechannel quality and/or speed. In one embodiment, the second group ofusers may be (dynamically) assigned to a second group of clusters, suchthat the users hop within the assigned group of clusters.

In one embodiment, a user from the first group of users, operating underCSS scheduling mode, may be reassigned to the second group of users,operating under FH mode, when at least one characteristic of such user,e.g., channel quality, mobility, Doppler effect, rate of issued NACKs,etc., is changed. In one embodiment, a group of clusters assigned forCSS may be reassigned for FH, or vice versa.

FIG. 2 shows one embodiment for implementing flexible frequency spectrumallocation to a plurality of diverse users. The grouping or associationof clusters enables a flexible bandwidth partitioning and/or allocationbetween the CSS-scheduled users and the FH-scheduled users. The clustersfrom the same and/or different segments may be grouped into groups ofcertain size N_(g). The group structure may be known to the accesspoints, some or all access terminals, or both. The grouping structuremay be fixed and each group may be specified by a group ID. Similar tothe cluster pattern set, as discussed above, grouping structure may bedifferent for different sectors/cells. A disparity of group structuresfor different sectors/cell may allow improved interference diversity.

In one embodiment, a channel assignment message may contain, besides theclusters ID and/or segment ID, a FH/CSS indicator or flag, e.g., aone-bit indicator, identifying a user, a group or users, and/or a groupof clusters for FH/CSS scheduling. In the case of CSS assignment, a userstays with the assigned cluster group(s) until a new assignment. In thecase of FH assignment, a user hops within the assigned cluster groups,according to a pre-defined hopping pattern, e.g., in the round robinfashion. In one embodiment, all the clusters within the same group areassigned either for CSS or for FH scheduling.

For the example shown in FIG. 2, the first group 202 may comprise thefirst cluster 204 of the first segment 206, the first cluster 208 of theK^(th) segment 210, and first cluster 212 of the (Ns−1)^(th) segment214. The second group 216 comprises the second cluster 224 of the firstsegment 206, the second cluster 228 of the (K+1)^(th) segment 230, andthe second cluster 232 of the (Ns−1)^(th) segment 214. As stated above,other group arrangements of the clusters may be used, e.g., differentclusters from different segments may be grouped together.

According to one embodiment, the first group 202 may be designated as aCSS-scheduled group, meaning that the users assigned to first group 202are fixedly assigned to the clusters in first group 202. This may be dueto the fact that such users are nonmoving or slow moving, whose channelquality may not noticeably change with time. According to oneembodiment, the second group 216 may be designated as a FH-scheduledgroup, meaning that the users assigned to second group 216 are(dynamically) assigned to the clusters in second group 216, such thatthe users my hop within the assigned group of clusters. This may be dueto the fact that such users are fast moving, whose channel quality mayrapidly change with time.

According to one embodiment, a group of users is assigned to the firstgroup of clusters 202. The assignment may be based on the user'schannels quality, as discussed above, e.g., user 1 may have high channelquality in the first segment 206, user 2 may have high channel qualityin the K^(th) segment 210, and user 3 may have high channel quality inthe (Ns−1)^(th) segment 214. If users 1, 2, and 3 are all scheduled forCSS, e.g., for being nonmoving or slow moving users, users 1, 2, and 3may be fixedly assigned to clusters 204, 208, and 212, respectively, infirst group 202.

According to one embodiment, users 4, 5, and 6 are assigned to thesecond group of clusters 216. However, if such users are fast movingusers having rapidly changing channel quality and/or speed, andaccordingly scheduled for FH, they may be dynamically assigned toclusters 224, 228, and 232, respectively, in the second group 216. Suchusers may hop from cluster to cluster within second group 216 accordingto a predetermined, or real-time configured, hopping scheme.

In one embodiment, when mobility, Doppler, or some other characteristicsof a user changes, the user may be reassigned to a different group, or aregrouping of the clusters may happen. In the above example, if users 2and 3 become fast moving, while users 4 and 5 become nonmoving or slowmoving, users 1, 4, and 5 may be fixedly assigned to clusters 204, 208,and 212, respectively, in the first group 202, and users 2, 3, and 6 maybe (dynamically) assigned to hop among the clusters 224, 228, and 232,respectively, in the second group 216. H is contemplated that differentnumber of groups and/or clusters may be used.

According to one cluster assignment, spectrum partitioning between CSSand FH users yields the granularity of N_(g) clusters. Hence, the choiceof N_(g) is a tradeoff between the minimum diversity order (Ng), on onehand, and the spectrum partitioning granularity of N_(g) clusters (Ng×Mctones), on the other hand. In one embodiment, a fairly small N_(g)ensures a satisfactory channel diversity and granularity ofpartitioning. For example, small group size allows low channel diversitybecause of small number of clusters to hop. However, large group size,which improves channel diversity, increases granularity, i.e., each timea new user demands a new group of cluster, a large number of tones(Ng×Mc) need to be added, which may cause inefficient channel bandwidthuse.

According to one embodiment, a number of clusters within a number ofcluster groups may be assigned to a user. To assign M clusters to asingle user by a single assignment message, M (consecutive) groups maybe used, while the precise cluster within each group may be identifiedby an ID specified in the assignment message. In this case, the clusterscorresponding to the (consecutive) groups may be interleaved infrequency to ensure frequency diversity within each channel.

For the exemplary grouping shown in FIG. 2, a user may be assigned tothe first cluster 204 of the first group 202 and the first cluster ofthe second group 216, i.e., M=2. If the user is scheduled for CSS, theuser may see diversity order of 2, i.e., the user is fixedly assigned toM=2 clusters 204, 224. However, if the user is scheduled for FH, theuser may see diversity order of 6, i.e., the user may hop among M=2groups of Ng=3 clusters each. For this choice of M=2 and Ng=3, FHprovides an acceptable interference diversity.

Now, consider the case that the user is assigned to the first cluster ofM=4 groups of clusters. If the user is scheduled to CSS, the user maysee diversity order of M=4, and if the user is scheduled to FH, the usermay see diversity of order of 12. Therefore, for the choice of M=4 andNg=3, either CSS or FH may provide a satisfactory interferencediversity. In one embodiment, a fast-moving user may be scheduled for FHmode when M<Ng, and for either CSS or FH mode when M>Ng.

FIG. 3 shows a block diagram of a access point 110 x and an accessterminal 120 x, for implementing flexible spectrum partitioning andallocation as discussed above in connection with FIG. 1 and FIG. 2. Forthe reverse link, at terminal 120 x, a transmit (TX) data processor 314receives traffic data from a data buffer 312, processes (e.g., encodes,interleaves, and symbol maps) each data packet based on a selectedcoding and modulation scheme, and provides data symbols. A data symbolis a modulation symbol for data, and a pilot symbol is a modulationsymbol for pilot (which is known a priori). A modulator 316 receives thedata symbols, pilot symbols, and possibly signaling for the reverselink, performs OFDM modulation and/or other processing as specified bythe system, and provides a stream of output chips. A transmitter unit(TMTR) 318 processes (e.g., converts to analog, filters, amplifies, andfrequency up converts) the output chip stream and generates a modulatedsignal, which is transmitted from an antenna 320.

At access point 110 x, the modulated signals transmitted by terminal 120x and other terminals in communication with access point 110 x arereceived by an antenna 352. A receiver unit (RCVR) 354 processes (e.g.,conditions and digitizes) the received signal from antenna 352 andprovides received samples. A demodulator (Demod) 356 processes (e.g.,demodulates and detects) the received samples and provides detected datasymbols, which are noisy estimate of the data symbols transmitted by theterminals to access point 110 x. A receive (RX) data processor 358processes (e.g., symbol demaps, deinterleaves, and decodes) the detecteddata symbols for each terminal and provides decoded data for thatterminal.

For the forward link, at access point 110 x, traffic data is processedby a TX data processor 360 to generate data symbols. A modulator 362receives the data symbols, pilot symbols, and signaling for the forwardlink, performs OFDM modulation and/or other pertinent processing, andprovides an output chip stream, which is further conditioned by atransmitter unit 364 and transmitted from antenna 352. The forward linksignaling may comprise power control commands generated by a controller370 for all terminals transmitting on the reverse link to base station110 x. At terminal 120 x, the modulated signal transmitted by basestation 110 x is received by antenna 320, conditioned and digitized by areceiver unit 322, and processed by a demodulator 324 to obtain detecteddata symbols. An RX data processor 326 processes the detected datasymbols and provides decoded data for the terminal and the forward linksignaling. Controller 330 receives the power control commands, andcontrols data transmission and transmits power on the reverse link toaccess point 110 x. Controllers 330 and 370 direct the operation ofterminal 120 x and access point 110 x, respectively. Memory units 332and 372 store program codes and data used by controllers 330 and 370,respectively, to implement the flexible spectrum partitioning and/orallocation as discussed above.

The disclosed embodiments may be applied to any one or combinations ofthe following technologies: Code Division Multiple Access (CDMA)systems, Multiple-Carrier CDMA (MC-CDMA), Wideband CDMA (W-CDMA),High-Speed Downlink Packet Access (HSDPA), Time Division Multiple Access(TDMA) systems, Frequency Division Multiple Access (FDMA) systems, andOrthogonal Frequency Division Multiple Access (OFDMA) systems.

The signaling transmission techniques described herein may beimplemented by various means. For example, these techniques may beimplemented in hardware, software, or a combination thereof. For ahardware implementation, the processing units used to process (e.g.,compress and encode) signaling may be implemented within one or moreapplication specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, micro-controllers, microprocessors,other electronic units designed to perform the functions describedherein, or a combination thereof. The processing units used to decodeand decompress the signaling may also be implemented with one or moreASICs, DSPs, and so on.

For a software implementation, the signaling transmission techniques maybe implemented with modules (e.g., procedures, functions, and so on)that perform the functions described herein. The software codes may bestored in a memory unit (e.g., memory unit 332 or 372 in FIG. 3) andexecuted by a processor (e.g., controller 330 or 370). The memory unitmay be implemented within the processor or external to the processor.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. A method for allocating a frequency spectrum to a plurality of users,the spectrum having a first number of segments, each segment having asecond number of clusters associated with a certain sector/cell, themethod comprising: assigning a first cluster of frequency sub-carrierswithin a first segment to a first user in a first sector/cell; andassigning a second cluster of frequency sub-carriers within a secondsegment to a second user in a second sector/cell, such that the firstcluster and the second cluster have different frequency sub-carrierassignment patterns.
 2. The method of claim 1, wherein assigning acluster within a segment to a user is based on channel quality of theuser.
 3. The method of claim 1, wherein the frequency spectrum comprisesa shared bandwidth allocated to a plurality of users in an OFDMAcommunication system.
 4. A method for allocating frequency spectrum to aplurality of users, the spectrum having a first number of segments, eachsegment having a second number of clusters associated with a certainsector, the method comprising: assigning a cluster of frequencysub-carriers to each of a plurality of users in a first sector/cell; andassigning a cluster of frequency sub-carriers to each of a plurality ofusers in a second sector/cell, such that each of the clusters assignedto the users in the first sector/cell has a different frequencysub-carrier assignment pattern with respect to each of the clustersassigned to the users in the second sector/cell.
 5. The method of claim4, wherein at least some of the clusters have noncontiguous sub-carrierassignment pattern.
 6. A method for partitioning a frequency spectrumfor allocation to a plurality of users, comprising: partitioning afrequency spectrum into a first number of segments, each segment havinga second number of frequency sub-carriers; and partitioning a thirdnumber of frequency sub-carriers of a segment to a fourth number ofclusters associated with a sector/cell, such that at least a fifthnumber of the clusters have non-overlapping frequency sub-carriersassignment patterns.
 7. The method of claim 6, wherein each of theclusters associated with a first sector/cell has different frequencysub-carriers assignment pattern with respect to a sixth number ofclusters associated with a second sector/cell.
 8. The method of claim 6,wherein each of the clusters associated with a first sector/cell isdifferent from each of the clusters associated with a second sector/cellin a same way.
 9. The method of claim 6, wherein at least some of theclusters have noncontiguous sub-carrier frequency assignment pattern.10. A method for flexibly allocating a frequency spectrum to a pluralityof users, the spectrum having a first number of segments, each segmenthaving a second number of clusters associated with a certain sector, themethod comprising: assigning a first group of clusters of frequencysub-carriers to a first group of users, the first group of users beingfixedly assigned to the first group of clusters; and assigning a secondgroup of clusters of frequency sub-carriers to a second group users, thesecond group of users hopping within the second group of clusters. 11.The method of claim 10, wherein a user is identified by a flagindicating whether the user is scheduled for fixed or hoppingassignment.
 12. The method of claim 10, wherein a group of clusters isidentified by a flag indicating whether the group of clusters isscheduled for fixed or hopping assignment.
 13. The method of claim 10,further comprising reassigning a user from the first group of users tothe second group of users, or a user from the second group of users tothe first group of users, as at least one characteristic of such user ischanged.
 14. The method of claim 12, wherein the characteristiccomprises mobility.
 15. The method of claim 10, wherein each of thefirst and second groups of clusters may be reassigned to a differentgroup of users, so that the first group of users may hop within thefirst group of clusters and the second group of users may stay withtheir respective assigned clusters within the second group of clusters.16. A method for flexibly allocating a frequency spectrum to a pluralityof users, the spectrum having a first number of segments, each segmenthaving a second number of clusters associated with a certainsector/cell, the method comprising: assigning a first number of clustersto each of a second number of groups; and assigning a user to at leastone cluster in each group.
 17. The method of claim 16, wherein the useris scheduled to hop among the first number of clusters when the secondnumber is smaller than the first number.
 18. The method of claim 16,wherein the user is scheduled to either hop among the first number ofclusters or stay fixed with the assigned clusters when the second numberis smaller than the first number.
 19. A computer-readable mediumembodying means for implementing a method for allocating a frequencyspectrum to a plurality of users, the spectrum having a first number ofsegments, each segment having a second number of clusters associatedwith a certain sector/cell, the method comprising: assigning a firstcluster of frequency sub-carriers within a first segment to a first userin a first sector/cell; and assigning a second cluster of frequencysub-carriers within a second segment to a second user in a secondsector/cell, such that the first cluster and the second cluster havedifferent frequency sub-carrier assignment patterns.
 20. The medium ofclaim 19, wherein assigning a cluster within a segment to a user isbased on channel quality of the user.
 21. The medium of claim 19,wherein the frequency spectrum comprises a shared bandwidth allocated toa plurality of users in an OFDMA communication system.
 22. Acomputer-readable medium embodying means for implementing a method forallocating frequency spectrum to a plurality of users, the spectrumhaving a first number of segments, each segment having a second numberof clusters associated with a certain sector, the method comprising:assigning a cluster of frequency sub-carriers to each of a plurality ofusers in a first sector/cell; and assigning a cluster of frequencysub-carriers to each of a plurality of users in a second sector/cell,such that each of the clusters assigned to the users in the firstsector/cell has a different frequency sub-carrier assignment patternwith respect to each of the clusters assigned to the users in the secondsector/cell.
 23. The medium of claim 22, wherein at least some of theclusters have noncontiguous sub-carrier assignment pattern.
 24. Acomputer-readable medium embodying means for implementing a method forpartitioning a frequency spectrum for allocation to a plurality ofusers, comprising: partitioning a frequency spectrum into a first numberof segments, each segment having a second number of frequencysub-carriers; and partitioning a third number of frequency sub-carriersof a segment to a fourth number of clusters associated with asector/cell, such that at least a fifth number of the clusters havenon-overlapping frequency sub-carriers assignment patterns.
 25. Themedium of claim 24, wherein each of the clusters associated with a firstsector/cell has different frequency sub-carriers assignment pattern withrespect to a sixth number of clusters associated with a secondsector/cell.
 26. The medium of claim 24, wherein each of the clustersassociated with a first sector/cell is different from each of theclusters associated with a second sector/cell in a same way.
 27. Themedium of claim 24, wherein at least some of the clusters havenoncontiguous sub-carrier frequency assignment pattern.
 28. Acomputer-readable medium embodying means for implementing a method forflexibly allocating a frequency spectrum to a plurality of users, thespectrum having a first number of segments, each segment having a secondnumber of clusters associated with a certain sector, the methodcomprising: assigning a first group of clusters of frequencysub-carriers to a first group of users, the first group of users beingfixedly assigned to the first group of clusters; and assigning a secondgroup of clusters of frequency sub-carriers to a second group users, thesecond group of users hopping within the second group of clusters. 29.The medium of claim 28, wherein a user is identified by a flagindicating whether the user is scheduled for fixed or hoppingassignment.
 30. The medium of claim 28, wherein a group of clusters isidentified by a flag indicating whether the group of clusters isscheduled for fixed or hopping assignment.
 31. The medium of claim 28,further comprising reassigning a user from the first group of users tothe second group of users, or a user from the second group of users tothe first group of users, as at least one characteristic of such user ischanged.
 32. The medium of claim 30, wherein the characteristiccomprises mobility.
 33. The medium of claim 28, wherein each of thefirst and second groups of clusters may be reassigned to a differentgroup of users, so that the first group of users may hop within thefirst group of clusters and the second group of users may stay withtheir respective assigned clusters within the second group of clusters.34. A computer-readable medium embodying means for implementing a methodfor flexibly allocating a frequency spectrum to a plurality of users,the spectrum having a first number of segments, each segment having asecond number of clusters associated with a certain sector/cell, themethod comprising: assigning a first number of clusters to each of asecond number of groups; and assigning a user to at least one cluster ineach group.
 35. The medium of claim 34, wherein the user is scheduled tohop among the first number of clusters when the second number is smallerthan the first number.
 36. The medium of claim 34, wherein the user isscheduled to either hop among the first number of clusters or stay fixedwith the assigned clusters when the second number is smaller than thefirst number.
 37. An apparatus for allocating a frequency spectrum to aplurality of users, the spectrum having a first number of segments, eachsegment having a second number of clusters associated with a certainsector/cell, comprising: means for assigning a first cluster offrequency sub-carriers within a first segment to a first user in a firstsector/cell; and means for assigning a second cluster of frequencysub-carriers within a second segment to a second user in a secondsector/cell, such that the first cluster and the second cluster havedifferent frequency sub-carrier assignment patterns.
 38. The apparatusof claim 37, wherein assigning a cluster within a segment to a user isbased on channel quality of the user.
 39. The apparatus of claim 37,wherein the frequency spectrum comprises a shared bandwidth allocated toa plurality of users in an OFDMA communication system.
 40. An apparatusfor allocating frequency spectrum to a plurality of users, the spectrumhaving a first number of segments, each segment having a second numberof clusters associated with a certain sector, comprising: means forassigning a cluster of frequency sub-carriers to each of a plurality ofusers in a first sector/cell; and means for assigning a cluster offrequency sub-carriers to each of a plurality of users in a secondsector/cell, such that each of the clusters assigned to the users in thefirst sector/cell has a different frequency sub-carrier assignmentpattern with respect to each of the clusters assigned to the users inthe second sector/cell.
 41. The apparatus of claim 40, wherein at leastsome of the clusters have noncontiguous sub-carrier assignment pattern.42. An apparatus for partitioning a frequency spectrum for allocation toa plurality of users, comprising: means for partitioning a frequencyspectrum into a first number of segments, each segment having a secondnumber of frequency sub-carriers; and means for partitioning a thirdnumber of frequency sub-carriers of a segment to a fourth number ofclusters associated with a sector/cell, such that at least a fifthnumber of the clusters have non-overlapping frequency sub-carriersassignment patterns.
 43. The apparatus of claim 42, wherein each of theclusters associated with a first sector/cell has different frequencysub-carriers assignment pattern with respect to a sixth number ofclusters associated with a second sector/cell.
 44. The apparatus ofclaim 42, wherein each of the clusters associated with a firstsector/cell is different from each of the clusters associated with asecond sector/cell in a same way.
 45. The apparatus of claim 42, whereinat least some of the clusters have noncontiguous sub-carrier frequencyassignment pattern.
 46. An apparatus for flexibly allocating a frequencyspectrum to a plurality of users, the spectrum having a first number ofsegments, each segment having a second number of clusters associatedwith a certain sector, comprising: means for assigning a first group ofclusters of frequency sub-carriers to a first group of users, the firstgroup of users being fixedly assigned to the first group of clusters;and means for assigning a second group of clusters of frequencysub-carriers to a second group users, the second group of users hoppingwithin the second group of clusters.
 47. The apparatus of claim 46,further comprising means for indicating whether the user is scheduledfor fixed or hopping assignment.
 48. The apparatus of claim 46, furthercomprising means for indicating whether a group of clusters is scheduledfor fixed or hopping assignment.
 49. The apparatus of claim 46, furthercomprising means for reassigning a user from the first group of users tothe second group of users, or a user from the second group of users tothe first group of users, as at least one characteristic of such user ischanged.
 50. The apparatus of claim 48, wherein the characteristiccomprises mobility.
 51. The apparatus of claim 46, further comprisingmeans for reassigning each of the first and second groups of clusters toa different group of users, so that the first group of users may hopwithin the first group of clusters and the second group of users maystay with their respective assigned clusters within the second group ofclusters.
 52. An apparatus for flexibly allocating a frequency spectrumto a plurality of users, the spectrum having a first number of segments,each segment having a second number of clusters associated with acertain sector/cell, comprising: means for assigning a first number ofclusters to each of a second number of groups; and means for assigning auser to at least one cluster in each group.
 53. The apparatus of claim52, further comprising means for scheduling the user to hop among thefirst number of clusters when the second number is smaller than thefirst number.
 54. The apparatus of claim 52, further comprising meansfor scheduling the user to either hop among the first number of clustersor stay fixed with the assigned clusters when the second number issmaller than the first number.
 55. At least one processor programmed toexecute a method for allocating a frequency spectrum to a plurality ofusers, the spectrum having a first number of segments, each segmenthaving a second number of clusters associated with a certainsector/cell, the method comprising: assigning a first cluster offrequency sub-carriers within a first segment to a first user in a firstsector/cell; and assigning a second cluster of frequency sub-carrierswithin a second segment to a second user in a second sector/cell, suchthat the first cluster and the second cluster have different frequencysub-carrier assignment patterns.
 56. The processor of claim 55, whereinassigning a cluster within a segment to a user is based on channelquality of the user.
 57. The processor of claim 55, wherein thefrequency spectrum comprises a shared bandwidth allocated to a pluralityof users in an OFDMA communication system.
 58. At least one processorprogrammed to execute a method for allocating frequency spectrum to aplurality of users, the spectrum having a first number of segments, eachsegment having a second number of clusters associated with a certainsector, the method comprising: assigning a cluster of frequencysub-carriers to each of a plurality of users in a first sector/cell; andassigning a cluster of frequency sub-carriers to each of a plurality ofusers in a second sector/cell, such that each of the clusters assignedto the users in the first sector/cell has a different frequencysub-carrier assignment pattern with respect to each of the clustersassigned to the users in the second sector/cell.
 59. The processor ofclaim 58, wherein at least some of the clusters have noncontiguoussub-carrier assignment pattern.
 60. At least one processor programmed toexecute a method for partitioning a frequency spectrum for allocation toa plurality of users, comprising: partitioning a frequency spectrum intoa first number of segments, each segment having a second number offrequency sub-carriers; and partitioning a third number of frequencysub-carriers of a segment to a fourth number of clusters associated witha sector/cell, such that at least a fifth number of the clusters havenon-overlapping frequency sub-carriers assignment patterns.
 61. Theprocessor of claim 60, wherein each of the clusters associated with afirst sector/cell has different frequency sub-carriers assignmentpattern with respect to a sixth number of clusters associated with asecond sector/cell.
 62. The processor of claim 60, wherein each of theclusters associated with a first sector/cell is different from each ofthe clusters associated with a second sector/cell in a same way.
 63. Theprocessor of claim 60, wherein at least some of the clusters havenoncontiguous sub-carrier frequency assignment pattern.
 64. At least oneprocessor programmed to execute a method for flexibly allocating afrequency spectrum to a plurality of users, the spectrum having a firstnumber of segments, each segment having a second number of clustersassociated with a certain sector, the method comprising: assigning afirst group of clusters of frequency sub-carriers to a first group ofusers, the first group of users being fixedly assigned to the firstgroup of clusters; and assigning a second group of clusters of frequencysub-carriers to a second group users, the second group of users hoppingwithin the second group of clusters.
 65. The processor of claim 64,wherein a user is identified by a flag indicating whether the user isscheduled for fixed or hopping assignment.
 66. The processor of claim64, wherein a group of clusters is identified by a flag indicatingwhether the group of clusters is scheduled for fixed or hoppingassignment.
 67. The processor of claim 64, the method further comprisingreassigning a user from the first group of users to the second group ofusers, or a user from the second group of users to the first group ofusers, as at least one characteristic of such user is changed.
 68. Theprocessor of claim 66, wherein the characteristic comprises mobility.69. The processor of claim 64, wherein each of the first and secondgroups of clusters may be reassigned to a different group of users, sothat the first group of users may hop within the first group of clustersand the second group of users may stay with their respective assignedclusters within the second group of clusters.
 70. At least one processorprogrammed to execute a method for flexibly allocating a frequencyspectrum to a plurality of users, the spectrum having a first number ofsegments, each segment having a second number of clusters associatedwith a certain sector/cell, the method comprising: assigning a firstnumber of clusters to each of a second number of groups; and assigning auser to at least one cluster in each group.
 71. The processor of claim70, wherein the user is scheduled to hop among the first number ofclusters when the second number is smaller than the first number. 72.The processor of claim 70, wherein the user is scheduled to either hopamong the first number of clusters or stay fixed with the assignedclusters when the second number is smaller than the first number.